Breasts: Anatomy

Gross Anatomy of the Breast

The breasts are paired organs on the anterior chest wall Chest wall The chest wall consists of skin, fat, muscles, bones, and cartilage. The bony structure of the chest wall is composed of the ribs, sternum, and thoracic vertebrae. The chest wall serves as armor for the vital intrathoracic organs and provides the stability necessary for the movement of the shoulders and arms. Chest Wall: Anatomy and are composed of modified apocrine sweat glands Sweat glands Sweat-producing structures that are embedded in the dermis. Each gland consists of a single tube, a coiled body, and a superficial duct. Soft Tissue Abscess arranged into lobules and ducts.

Location and structure

Location:

• Anterior thoracic wall
• Overlying the deep fascia Fascia Layers of connective tissue of variable thickness. The superficial fascia is found immediately below the skin; the deep fascia invests muscles, nerves, and other organs. Cellulitis and pectoral muscles
• At the level of ribs Ribs A set of twelve curved bones which connect to the vertebral column posteriorly, and terminate anteriorly as costal cartilage. Together, they form a protective cage around the internal thoracic organs. Chest Wall: Anatomy 2–6, from the sternum Sternum A long, narrow, and flat bone commonly known as breastbone occurring in the midsection of the anterior thoracic segment or chest region, which stabilizes the rib cage and serves as the point of origin for several muscles that move the arms, head, and neck. Chest Wall: Anatomy to the midaxillary line Midaxillary Line Examination of the Breast, with the nipple Nipple The conic organs which usually give outlet to milk from the mammary glands. Examination of the Breast in the 4th intercostal space

Structure:

• Paired, tear-shaped, and of varying size
• Each composed of a mammary gland surrounded by connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue: Histology
• Components from internal to external:
  • Mammary gland: modified apocrine sweat gland arranged into lobules and ducts
  • Adipose tissue Adipose tissue Adipose tissue is a specialized type of connective tissue that has both structural and highly complex metabolic functions, including energy storage, glucose homeostasis, and a multitude of endocrine capabilities. There are three types of adipose tissue, white adipose tissue, brown adipose tissue, and beige or “brite” adipose tissue, which is a transitional form. Adipose Tissue: Histology: 80% of the breast in nonbreastfeeding woman
  • Nipple Nipple The conic organs which usually give outlet to milk from the mammary glands. Examination of the Breast–areolar complex: glandular (lactiferous) ducts converge and open to the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions in the mammary papilla ( nipple Nipple The conic organs which usually give outlet to milk from the mammary glands. Examination of the Breast), surrounded by the areola Areola Examination of the Breast (circular area of darker pigmentation), which contains sebaceous Montgomery glands to lubricate and protect the nipple Nipple The conic organs which usually give outlet to milk from the mammary glands. Examination of the Breast during breastfeeding Breastfeeding Breastfeeding is often the primary source of nutrition for the newborn. During pregnancy, hormonal stimulation causes the number and size of mammary glands in the breast to significantly increase. After delivery, prolactin stimulates milk production, while oxytocin stimulates milk expulsion through the lactiferous ducts, where it is sucked out through the nipple by the infant. Breastfeeding.
• Ligaments and supporting structures:
  • Deep pectoral fascia Fascia Layers of connective tissue of variable thickness. The superficial fascia is found immediately below the skin; the deep fascia invests muscles, nerves, and other organs. Cellulitis: attachment of the breast to the pectoralis major muscle. The space between the breast and muscle is the retromammary space.
  • Suspensory ligaments of the breast (Cooper ligaments): run between the pectoral fascia Fascia Layers of connective tissue of variable thickness. The superficial fascia is found immediately below the skin; the deep fascia invests muscles, nerves, and other organs. Cellulitis and the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions, between the secretory lobules

Development

• Begins as a thickening of the chest wall Chest wall The chest wall consists of skin, fat, muscles, bones, and cartilage. The bony structure of the chest wall is composed of the ribs, sternum, and thoracic vertebrae. The chest wall serves as armor for the vital intrathoracic organs and provides the stability necessary for the movement of the shoulders and arms. Chest Wall: Anatomy, leading to the mammary ridge, or milk line  
• Nipples and breast duct system are present at birth.
• Further development during puberty Puberty Puberty is a complex series of physical, psychosocial, and cognitive transitions usually experienced by adolescents (11-19 years of age). Puberty is marked by a growth in stature and the development of secondary sexual characteristics, achievement of fertility, and changes in most body systems. Puberty is under the influence of female sex Sex The totality of characteristics of reproductive structure, functions, phenotype, and genotype, differentiating the male from the female organism. Gender Dysphoria hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types.
• Breast size increases during pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care and reduces after menopause Menopause Menopause is a physiologic process in women characterized by the permanent cessation of menstruation that occurs after the loss of ovarian activity. Menopause can only be diagnosed retrospectively, after 12 months without menstrual bleeding. Menopause

Microscopic Anatomy of the Mammary Gland

The mammary gland is composed of modified apocrine sweat glands Sweat glands Sweat-producing structures that are embedded in the dermis. Each gland consists of a single tube, a coiled body, and a superficial duct. Soft Tissue Abscess divided into lobules, which reach the nipple Nipple The conic organs which usually give outlet to milk from the mammary glands. Examination of the Breast via lactiferous ducts. The ducts are composed of epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology surrounded by myoepithelial cells.

• Mammary gland: milk-producing modified apocrine sweat gland consisting of 15–20 lobes, further divided into lobules connected to the nipple Nipple The conic organs which usually give outlet to milk from the mammary glands. Examination of the Breast by lactiferous ducts:
  • Lobules:
    • Milk-producing glands
    • Composed of alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) lined with cuboidal epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology surrounded by contractile myoepithelial cells
  • Lactiferous ducts:
    • Passage from alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) to nipple Nipple The conic organs which usually give outlet to milk from the mammary glands. Examination of the Breast
    • Dilation at the ends (lactiferous sinuses) function as milk reservoirs.
  • Stroma: adipose tissue Adipose tissue Adipose tissue is a specialized type of connective tissue that has both structural and highly complex metabolic functions, including energy storage, glucose homeostasis, and a multitude of endocrine capabilities. There are three types of adipose tissue, white adipose tissue, brown adipose tissue, and beige or “brite” adipose tissue, which is a transitional form. Adipose Tissue: Histology and suspensory ligaments surround and separate the lobules and ducts.
• Ductal system: epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology surrounded by myoepithelial cells
  • Lobule → terminal or lactiferous ducts → major ducts →  terminal ducts →  lactiferous sinus (milk reservoir Reservoir Animate or inanimate sources which normally harbor disease-causing organisms and thus serve as potential sources of disease outbreaks. Reservoirs are distinguished from vectors (disease vectors) and carriers, which are agents of disease transmission rather than continuing sources of potential disease outbreaks. Humans may serve both as disease reservoirs and carriers. Escherichia coli) → open into nipple Nipple The conic organs which usually give outlet to milk from the mammary glands. Examination of the Breast
• Prolactin, progesterones, and estrogens stimulate the proliferation and growth of the breast’s secretory units.

Neurovasculature

The arterial supply to the breast is via branches of the subclavian, axillary, and intercostal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology with venous drainage into the subclavian, axillary, and azygos veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins: Histology. The innervation is from branches of the 2nd–6th intercostal nerves, with hormonal input via prolactin.

Lymphovascular supply

• Arterial supply:
  • Medial breast: internal thoracic artery, which is a branch of the subclavian artery
  • Lateral breast:
    • Lateral thoracic/abdominal branches from the axillary artery Axillary Artery The continuation of the subclavian artery; it distributes over the upper limb, axilla, chest and shoulder. Axilla and Brachial Plexus: Anatomy
    • Mammary branches from the intercostal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology
• Venous drainage:
  • Accompany the mentioned arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology
  • Drain into the subclavian, axillary, and azygos veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins: Histology
• Lymphatic drainage: lymph Lymph The interstitial fluid that is in the lymphatic system. Secondary Lymphatic Organs from the breast lobules, nipple Nipple The conic organs which usually give outlet to milk from the mammary glands. Examination of the Breast, and areola Areola Examination of the Breast → subareolar lymphatic plexus:
  • 75% → pectoral lymph nodes Lymph Nodes They are oval or bean shaped bodies (1 – 30 mm in diameter) located along the lymphatic system. Lymphatic Drainage System: Anatomy → axillary lymph nodes Lymph Nodes They are oval or bean shaped bodies (1 – 30 mm in diameter) located along the lymphatic system. Lymphatic Drainage System: Anatomy → subclavian lymphatic trunks; important pathway for metastatic spread of breast carcinomas
  • 20% → parasternal nodes → bronchomediastinal trunks
  • 5% → intercostal nodes → thoracic or bronchomediastinal lymph Lymph The interstitial fluid that is in the lymphatic system. Secondary Lymphatic Organs trunks

Innervation

• Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology and sympathetic fibers: supraclavicular nerves ( cervical plexus Cervical Plexus A network of nerve fibers originating in the upper four cervical spinal cord segments. The cervical plexus distributes cutaneous nerves to parts of the neck, shoulders, and back of the head. It also distributes motor fibers to muscles of the cervical spinal column, infrahyoid muscles, and the diaphragm. Peripheral Nerve Injuries in the Cervicothoracic Region) and branches of the 2nd–6th intercostal nerves
• Lactation Lactation The processes of milk secretion by the maternal mammary glands after parturition. The proliferation of the mammary glandular tissue, milk synthesis, and milk expulsion or let down are regulated by the interactions of several hormones including estradiol; progesterone; prolactin; and oxytocin. Breastfeeding: stimulated by prolactin 

Clinical Relevance

• Mammography Mammography Radiographic examination of the breast. Breast Cancer Screening: allows for early detection of breast cancer Breast cancer Breast cancer is a disease characterized by malignant transformation of the epithelial cells of the breast. Breast cancer is the most common form of cancer and 2nd most common cause of cancer-related death among women. Breast Cancer or precancerous Precancerous Pathological conditions that tend eventually to become malignant. Barrett Esophagus lesions before they develop into invasive breast cancer Breast cancer Breast cancer is a disease characterized by malignant transformation of the epithelial cells of the breast. Breast cancer is the most common form of cancer and 2nd most common cause of cancer-related death among women. Breast Cancer. It is recommended to start routine annual mammography Mammography Radiographic examination of the breast. Breast Cancer Screening screening Screening Preoperative Care after the age of 40 years. 
• Fibrocystic Fibrocystic Fibrocystic Change changes: benign Benign Fibroadenoma changes that mimic but do not achieve the threshold Threshold Minimum voltage necessary to generate an action potential (an all-or-none response) Skeletal Muscle Contraction to be considered malignant conditions of the breast. Fibrocystic Fibrocystic Fibrocystic Change changes are those that may be seen even in normal breast tissue.
• Mastitis Mastitis Mastitis is inflammation of the breast tissue with or without infection. The most common form of mastitis is associated with lactation in the first few weeks after birth. Non-lactational mastitis includes periductal mastitis and idiopathic granulomatous mastitis (IGM). Mastitis: inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of mammary gland tissue, which can be lactational or nonlactational. Individuals will present with warmth and tenderness of the inflamed area. First-line treatment consists of beta-lactam Beta-Lactam Penicillins antibiotics, such as dicloxacillin Dicloxacillin One of the penicillins which is resistant to penicillinase. Penicillins.
• Fat necrosis Necrosis The death of cells in an organ or tissue due to disease, injury or failure of the blood supply. Ischemic Cell Damage: benign Benign Fibroadenoma condition. Fat necrosis Necrosis The death of cells in an organ or tissue due to disease, injury or failure of the blood supply. Ischemic Cell Damage can occur anywhere in the breast and can affect women of any age. This condition is characterized by a firm, round lump, which is usually painless, but it may present with tenderness or pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways.
• Gynecomastia Gynecomastia Gynecomastia is a benign proliferation of male breast glandular ductal tissue, usually bilateral, caused by increased estrogen activity, decreased testosterone activity, or medications. The condition is common and physiological in neonates, adolescent boys, and elderly men. Gynecomastia: benign Benign Fibroadenoma enlargement of breasts in males due to glandular proliferation, giving breasts a characteristic rubbery nature. Gynecomastia Gynecomastia Gynecomastia is a benign proliferation of male breast glandular ductal tissue, usually bilateral, caused by increased estrogen activity, decreased testosterone activity, or medications. The condition is common and physiological in neonates, adolescent boys, and elderly men. Gynecomastia can be caused by medications that elevate estrogen Estrogen Compounds that interact with estrogen receptors in target tissues to bring about the effects similar to those of estradiol. Estrogens stimulate the female reproductive organs, and the development of secondary female sex characteristics. Estrogenic chemicals include natural, synthetic, steroidal, or non-steroidal compounds. Ovaries: Anatomy levels, such as cimetidine Cimetidine A histamine congener, it competitively inhibits histamine binding to histamine h2 receptors. Cimetidine has a range of pharmacological actions. It inhibits gastric acid secretion, as well as pepsin and gastrin output. Antihistamines.
• Fibroadenoma Fibroadenoma Fibroadenomas are the most common benign tumor of the female breast and the most common breast tumor in adolescent and young women. The tumors are well-circumscribed, mobile, and unencapsulated, with a rubbery or firm consistency. Fibroadenoma: benign Benign Fibroadenoma breast masses that are usually mobile on palpation Palpation Application of fingers with light pressure to the surface of the body to determine consistency of parts beneath in physical diagnosis; includes palpation for determining the outlines of organs. Dermatologic Examination. Fibroadenomas are commonly identified in young women and represent a diagnostic challenge for surgeons. Fibroadenomas do not typically turn into breast cancer Breast cancer Breast cancer is a disease characterized by malignant transformation of the epithelial cells of the breast. Breast cancer is the most common form of cancer and 2nd most common cause of cancer-related death among women. Breast Cancer, so it is safe to just monitor these masses.
• Breast cancer Breast cancer Breast cancer is a disease characterized by malignant transformation of the epithelial cells of the breast. Breast cancer is the most common form of cancer and 2nd most common cause of cancer-related death among women. Breast Cancer: Mastocarcinoma is a malignant tumor Tumor Inflammation of the mammary gland. The point of origin may be either the mammary gland’s ducts or lobules, leading to ductal carcinoma and lobular carcinoma, respectively. Breast cancer Breast cancer Breast cancer is a disease characterized by malignant transformation of the epithelial cells of the breast. Breast cancer is the most common form of cancer and 2nd most common cause of cancer-related death among women. Breast Cancer is treated with surgical excision +/– radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma and chemotherapy Chemotherapy Osteosarcoma.
• Nipple Nipple The conic organs which usually give outlet to milk from the mammary glands. Examination of the Breast discharge: In nonlactating women, nipple Nipple The conic organs which usually give outlet to milk from the mammary glands. Examination of the Breast discharge can be classified as either galactorrhea Galactorrhea Excessive or inappropriate lactation in females or males, and not necessarily related to pregnancy. Galactorrhea can occur either unilaterally or bilaterally, and be profuse or sparse. Its most common cause is hyperprolactinemia. Hyperprolactinemia or nonmilky nipple Nipple The conic organs which usually give outlet to milk from the mammary glands. Examination of the Breast discharge. Galactorrhea Galactorrhea Excessive or inappropriate lactation in females or males, and not necessarily related to pregnancy. Galactorrhea can occur either unilaterally or bilaterally, and be profuse or sparse. Its most common cause is hyperprolactinemia. Hyperprolactinemia is usually caused by endocrine disorders or medications, whereas nonmilky nipple Nipple The conic organs which usually give outlet to milk from the mammary glands. Examination of the Breast discharge is usually linked to benign Benign Fibroadenoma tumors.